# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Appeal to forum members to collect data
From: Alexandre Eremenko
Date: 2007 Oct 25, 15:59 -0400

```
Dear Henry,

> the use of Frank's on-line calculator
> as a standard to determine error.

I use it for several years, compared it with programs
written by myself and with hand calculation,
the calculator seems fine, though of course
I cannot guarantee.

Of course you can use any other method.
But. To make sure that our results are independent
of the method used, can you CHECK the result
with the Frank calculator before sending it to Jim?

This takes just few seconds per sight.
1. We will be sure that the results are reduced with one
uniform method.
2. If you find a disagreement between your calculation
and Frank's calculator, you will either find a bug
in Frank's calculator (to the benefit of all us who use it)

So this seems to be a win-win game:-)

> at very least it is rounded off to tenths
> which in itself leads to possible comparitive errors.

As I understand he keeps one extra digit in the calculation
and then only rounds the final result.
How many digits do you propose to keep in the final result?

> In my view, a purpose of the Lunar Observation was to
> determine Longitude based on time difference.

Not only. Also to control chronometer.

> It appears that a truer
> gauge of error would rest in a comparison of Lunar
> determined Longitude with the known position of
> observation.

With this I disagree. The error in position consists
of several components. These components have different
nature and magnitude. It is always easier (and more useful)
to analyse these components separately.
In fact the very word "analysis" means something like
"breaking into components".

> There really should be no problem with
> the actual distance measurement itself, given a decent
> instrument and a reasonably competent observer.

Jim and I (if I understand Jim's intention correctly)
are trying to analyse EXACTLY this: the measurement
of the distance itself. By a reasonably competent
observers with decent instruments.

So our points of view differ.
From my point of view, reduction and finding a position
is relatively trivial (and less interesting) matter
than the process of measurement itself.

Alex.

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